Surtseyan style eruption in the Ambae (Vanuatu,New Hebrides) caldera lake in 2005 December and its implication to volcanic hazards and emergency management on an ocean island.

No abstract availabl

Syn- and post-eruptive erosion, gully formation, and morphological evolution of a tephra ring in tropical climate erupted in 1913 in West Ambrym, Vanuatu

Syn- and post-eruptive erosion of volcanic cones plays an important role in mass redistribution of tephra over short periods. Descriptions of the early stages of erosion of tephra from monogenetic volcanic cones are rare, particularly those with a well-constrained timing of events. In spite of this lack of data, cone morphologies and erosion features are commonly used for long-term erosion rate calculations and relative age determinations in volcanic fields. Here we provide new constraints on the timing and nature of erosion from a tephra ring erupted in 1913 in West Ambrym, Vanuatu and exposed along a continuous 2.5 km long coastal section. The ring surrounds an oval shaped depression filled by water. It is composed of a succession of a phreatomagmatic fall and base surge beds, interbedded with thin scoriaceous lapilli units. Toward the outer edges of the ring, base-surge beds are gradually replaced in the succession by fine-ash dominated debris-flows and hyperconcentrated-flow deposits. The inter-fingering of phreatomagmatic deposits with syn-volcanic reworked volcaniclastic sediments indicates an ongoing remobilisation of freshly deposited tephra already during the eruption. Gullies cut into the un-weathered tephra are up to 4 m deep and commonly have c. 1 m of debris-flow deposit fill in their bases. There is no indication of weathering, vegetation fragments or soil development between the gully bases and the basal debris flow fills. Gully walls are steep and superficial fans of collapsed sediment are common. Most gullies are heavily vegetated although some active (ephemeral) channels occur. Hence, we conclude that the majority of the erosion of such tephra rings in tropical climates takes place directly during eruption and possibly for only a period of days to weeks afterward. After establishment of the gully network, tephra remobilisation is concentrated only within them. Therefore the shape of the erosion-modified volcanic landform is predominantly developed shortly after the eruption ceases. This observation indicates that gully erosion morphology may not necessarily relate to age of such a landform. Different intensities of erosion during eruption (related to water supply or rainfall) are probably the major influence on gully spacing, modal depth and form. Longer-term post-eruption processes that could be indicators of relative age may include internal gully deepening (below basal debris-flow fill sediments) and possibly widening and side-slope lowering due to undercutting and side-collapse

Perceived Family Support, Acculturation, and Life Satisfaction in Mexican American Youth: A Mixed-Methods Exploration

In this article, the authors describe a mixed-methods study designed to explore perceived family support, acculturation, and life satisfaction among 266 Mexican American adolescents. Specifically, the authors conducted a thematic analysis of open-ended responses to a question about life satisfaction to understand participants’ perceptions of factors that contributed to their overall satisfaction with life. The authors also conducted hierarchical regression analyses to investigate the independent and interactive contributions of perceived support from family and Mexican and Anglo acculturation orientations on life satisfaction. Convergence of mixed-methods findings demonstrated that perceived family support and Mexican orientation were significant predictors of life satisfaction in these adolescents. Implications, limitations, and directions for further research are discussed

Phreatomagmatic volcanic hazards where rift-systems meet the sea, a study from Ambae Island, Vanuatu

Uncorrected proofAmbae Island is a mafic stratovolcano located in the northern Vanuatu volcanic arc and has a NE–SW rift-controlled elongated shape. Several hundred scoria cones and fissure-fed lava fields occur along its long axis. After many decades of quiescence, Ambae Island erupted on the 28th of November 2005, disrupting the lives of its 10,000 inhabitants. Its activity remained focused at the central (crater-lake filled) vent and this is where hazard-assessments were focused. These assessments initially neglected that maars, tephra cones and rings occur at each tip of the island where the eruptive activity occurred b500 and b300 yr B.P. The products of this explosive phreatomagmatic activity are located where the rift axis meets the sea. At the NE edge of the island five tephra rings occur, each comparable in size to those on the summit of Ambae. Along the NE coastline, a near-continuous cliff section exposes an up to 25 m thick succession of near-vent phreatomagmatic tephra units derived from closely spaced vents. This can be subdivided into two major lithofacies associations. The first association represents when the locus of explosions was below sea level and comprises matrix-supported, massive to weakly stratified beds of coarse ash and lapilli. These are dominant in the lowermost part of the sequence and commonly contain coral fragments, indicating that the loci of explosion were located within a reef or coral sediment near the syn-eruptive shoreline. The second type indicate more stable vent conditions and rapidly repeating explosions of high intensity, producing fine-grained tephra with undulatory bedding and cross-lamination as well as megaripple bedforms. These surge and fall beds are more common in the uppermost part of the succession and form a few-m-thick pile. An older tephra succession of similar character occurs below, and buried trees in growth position, as well as those flattened within base surge beds. This implies that the centre of this eruption was very near the coastline. The processes implied by these deposits are amongst the most violent forms of volcanism on this island. In addition, the lowland and coastal areas affected by these events are the most heavily populated. This circumstance is mirrored on many similar volcanic islands, including the nearby SW Pacific examples of Taveuni (Fiji), Upolu and Savai'i (Samoa), and Ambrym (Vanuatu). These locations are paradoxically often considered safe areas during summit/central-vent eruptions, simply because they are farthest from the 34 central sources of ash-fall and lahar hazard. The observations presented here necessitate a revision of this view

Lava lakes and shallow level magmatic feeding systems of mafic volcanoes of an ocean island: Ambrym, Vanuatu (New Hebrides), South Pacific

Ambrym is an active volcanic island with 2 major vent complexes; Marum and Benbow. These vent complexes are continuously active over at least the past two thousands of years. These active vents either produce constant degassing during quite periods or sub-Plinian to Vulcanian explosive eruptions commonly influenced by magma-water interaction triggered phreatomagmatic explosive phases. The active vents of Ambrym perfectly expos inner walls of the crater/conduit transition zone, allowing to study in cross sectional view of the interbedded coherent magmatic bodies with pyroclastic successions. In the inner crater/conduit wall of the Marum volcano, that consists of at least 3 major vents, as well as a vent that is located on its flank (Niri Taten) exposes solidified complex lava lake cross-sections, lava spatter cone feeding lava pods, shallow intrusions as well as large sills that connected through a complex network of pathways to the surface and/or into the pyroclastic edifice of the volcano. This suggests that shallow level infiltration of melt into a mafic volcano plays an important role in the edifice growth